1. Field of the Invention
The present invention relates to disk drives for computer systems. More particularly, the present invention relates to a disk drive adjusting operating mode based on historical proximity of host commands.
2. Description of the Prior Art
Disk drives comprise one or more disks having a plurality of tracks which are partitioned into a number of data sectors. A head coupled to a distal end of an actuator arm is actuated over the disk to access a target data sector by rotating the actuator arm about a pivot in a seek operation. The disk drive typically employs a voice coil motor (VCM) for rotating the actuator arm about the pivot by energizing the voice coil with current. The ability of the VCM to follow a predetermined seek profile depends on the acceleration/deceleration capability of the VCM as controlled by the magnitude of current energizing the voice coil. Aggressive seek profiles require aggressive acceleration/deceleration currents which increases the heat and mechanical stress on the VCM, as well as increases power dissipation.
Disk drives are typically accessed in one of a number of modes, such as random access mode and proximity access mode. Random access mode occurs when the host is executing an application that accesses data in a substantially random manner, meaning the data may be recorded at random locations about the disk requiring numerous random length seeks. Proximity access mode occurs when the host is executing an application that accesses data recorded in close proximity on the disk, such as data accessed in a substantially sequential or near-sequential manner (e.g., when accessing a data-base or a video stream). When operating in a proximity access mode, performance is enhanced through predictive caching wherein a predetermined number of additional data sectors preceding and/or following the target data sectors are also read from the disk and stored in a cache memory in anticipation that these data sectors may also be requested by the host. If so, the access time of the disk drive is reduced significantly since the access time of the cache memory is much faster than the access time of the disk due to the mechanical latency in seeking the head and rotating the disk.
Certain performance benefits are attained by configuring the disk drive relative to the access mode. For example, if the disk drive is operating in a random access mode, it may be desirable to disable predictive caching to allow less aggressive seek profiles, thereby reducing VCM heating and power dissipation. There is, therefore, a need to detect the access mode of a disk drive so that it can be configured to improve operating performance.